Only 7 days of recumbency has been shown to result in rapid loss of muscle mass. More prolonged periods of bed rest have resulted in 30% reduction of muscle volume, particularly in muscles of the lower limbs.34 Studies examining the effect of immobilization on skeletal muscle have shown a disruption in the balance between protein synthesis and breakdown in which muscle protein anabolism is reduced and catabolism is increased.34 Studies conducted on immobilized animals have demonstrated that the damage caused to skeletal muscle is associated with activation

of various proteolytic systems which are further Inhibitors,research,lifescience,medical activated in muscles of old animals in comparison with young animals.35 For instance, increased ubiquitination of myosin heavy chain (MyHC) protein was observed in muscles of old immobilized animals in comparison with young immobilized animals.35 Bar-Shai et al.36,37 have suggested that activation of extracellular hydrolytic and proteolytic systems differ in muscles of old animals compared to young animals during immobilization. A different activation Inhibitors,research,lifescience,medical pattern of nuclear factor kB (NF-kB) in muscle atrophy was Inhibitors,research,lifescience,medical observed in which the canonic activation pathway of NF-kB was more prominent in muscles from old animals compared to young ones. Also, the involvement of growth hormone in muscular damage and atrophy during limb immobilization was demonstrated

by Carmeli et al.38 It was shown that administration of growth hormone to old rats significantly reduced muscle weight loss and atrophy, protein oxidation, and fiber disorientation caused by immobilization. Since low physical activity and sedentary lifestyle are main causes of sarcopenia, exercise Inhibitors,research,lifescience,medical is a primary strategy in the prevention and treatment of sarcopenia. Both aerobic training and resistance training can improve the rate of decline in muscle mass and strength with age.3 Aerobic training, in which large groups of muscle move for a prolonged period of time, is less likely to contribute to

Inhibitors,research,lifescience,medical muscle hypertrophy; however, it can increase the cross-sectional area of muscle fibers, mitochondrial volume, and enzyme activity. Also, aerobic exercise can reduce intramuscular fat and improve muscle functionality.3 Interestingly, several studies have demonstrated the anabolic others effects of aerobic training. Robinson et al.39 have shown that 6 weeks of aerobic training in older adults resulted in increased KRX-0401 cost long-term synthesis of muscle protein and DNA in comparison with young sedentary subjects. Pasini et al.40 have examined the effect of aerobic treadmill exercise on muscle anabolic pathways in young versus old rats. They have found that aerobic training ameliorated aging-associated impairments in muscle anabolic pathways, affecting the insulin and mTOR signaling pathways.38 In addition, Timmerman et al.41 have reported that aerobic training in older adults improves nutrient delivery to muscle, thus inducing an increased anabolic effect of nutrient intake.